WASHINGTON, Feb 13 (Reuters) - Environmentalists and industry groups ramped up efforts on Wednesday to influence the White House's decision on the Keystone XL pipeline project, a day after President Barack Obama said he would take action to curb climate-warming emissions.

A small group of activists and celebrities protested in front of the White House to put pressure on Obama to reject the controversial proposed crude oil pipeline. Among the 48 protesters arrested and released on ${esc.dollar}100 bail were actress Daryl Hannah and environmentalist Robert F. Kennedy Jr. and his son Conor Kennedy, said Maggie Kao, spokeswoman for the Sierra Club.

The action came before a rally planned for Sunday on Washington's National Mall, which organizers have dubbed "the largest climate rally in history."

The TransCanada Corp pipeline would transport 830,000 barrels of crude from the oil sands of northern Alberta, the world's third largest crude resource, to refineries and ports in Texas. TransCanada has been waiting for approval for 4 1/2 years.

Environmentalists say approval of the pipeline will encourage more development in the oil sands, where extraction is carbon-intensive, leading to greater greenhouse gas emissions.

The State Department in the coming days is due to issue a new environmental impact statement on the project, which is expected to guide the White House as it decides whether to give the project the go-ahead.

Obama had been widely expected to approve the pipeline after the governor of Nebraska approved a revised route through his state that avoided ecologically sensitive areas and aquifers.

But doubts rose after Obama put surprising emphasis on climate change in his January inaugural address, leading pipeline watchers to question whether the president would heed pressure from environmentalists.

Still, Canada's natural resources minister said on Wednesday he was cautiously optimistic Washington would approve the pipeline.

The American Petroleum Institute, the country's biggest oil and gas lobbying group, and some labor unions said they were also confident that Obama would approve Keystone.

"This is the one of the most scrutinized infrastructure projects in our nation's history," Sean McGarvey, president of building and construction at the AFL-CIO labor organization.

"The president has thoughtfully and methodically looked at this issue. I have no doubt that the president will make the right decision."

Many environmental groups welcomed Obama's focus on climate change in Tuesday's State of the Union speech. But some warned the Keystone decision would be more meaningful.

"I'm glad to see the president, after the long, odd silence of the campaign, ratcheting up the rhetoric about climate change," said Bill McKibben, founder of environmental group 350.org, who was among those arrested outside the White House on Wednesday. "The test of that rhetoric will be what he does about the purest, simplest test: the Keystone XL pipeline."

The American Petroleum Institute is also stepping up pressure on Obama to approve Keystone, which its members say will create more jobs and help ensure U.S. energy security. The group plans a national advertising campaign and "grassroots events across the country," urging Obama to approve the project.

Republican lawmakers, including House of Representatives Speaker John Boehner, have called on the president not to delay the decision further.

TRADE-OFFS

Some policy analysts speculate that Obama could announce other carbon-cutting measures if he were to approve the pipeline.

Joshua Saks, legislative director at the National Wildlife Federation, rejected such a trade-off.

"You can't do something else to mitigate the enormous effects of passing the Keystone pipeline," he said.

But Paul Bledsoe, an energy consultant who served on the White House Climate Change Task Force under President Bill Clinton, said Obama should roll out sweeping regulations targeting emissions at power plants, which account for one-third of U.S. greenhouse gas emissions, if he approves the pipeline.

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